Automatic transmission is widely used in automobiles, electric vehicle, construction machinery and the like. The conventional automatic transmission can be classified mainly as the following four types: Automatic Transmission (AT), Continuously Variable Transmission (CVT), Automated Manual Transmission (AMT) and Dual Clutch Transmission (DCT). The shifting process of above four types of automatic transmission are all controlled by an electrically controlled hydraulic servo device comprising a hydraulic pump, a plurality of hydraulic valves, a plurality of hydraulic clutches and a plurality of brakes, etc, which involves complex structure, high cost and high energy consumption.
With widespread application of such technologies as automobile electronic, automatic control and automobile network communication, the X-by-wire technique has become the tendency of vehicle development in the future. The X-by-wire technique is one that replaces mechanical and hydraulic system with electric wires, electronic controllers and wire control actuators by converting the driver's manipulation into electrical signals with a sensor; the electrical signals is input to an electric control unit where a control signal is generated to drive wire control actuators to perform a desired operation. Therefore, developing a new X-by-wire automatic transmission helps reduce the number of parts, cost and energy consumption and improve transmission efficiency.
A Chinese patent application No. CN201410469568.8 titled “multi-speed ring-arranged control-by-wire automatic transmission” and a patent application No. CN201410468564.8 titled “the double-level multi-speed control-by-wire automatic transmission” was published on Jan. 21, 2015; a Chinese patent application No. CN201410469720.2 titled “electric vehicle three-gear control-by-wire automatic transmission” and a patent application No. CN201410471726.3 titled “electric vehicle multi-speed control-by-wire automatic transmission” was published on Mar. 4, 2015; a Chinese patent application No. CN201520311494.5 titled “multi-speed control-by-wire automatic transmission” was published on Oct. 28, 2015. The published patents above have no hydraulic shifting elements, with the transmission gears of each gear normally engaged, and on the transmission path of each gear, there is provided an electromagnetic clutch respectively, whose engagement and disengagement are controlled by an electric control unit, thereby performing a shift-by-wire process. However, in each of the above patents, the electromagnetic clutch used in the shift-by-wire process has such disadvantages as bulky volume, low rotation speed and requirement for large power consumption. Therefore, the X-by-wire automatic transmission is large in size, low in rotational speed and large in the operation energy consumption.